 /*******************************************************************************
  * Copyright (c) 2006 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  ******************************************************************************/

 package org.eclipse.ui.internal.navigator.dnd;

 import java.lang.ref.WeakReference ;
 import java.util.HashSet ;
 import java.util.Iterator ;
 import java.util.Set ;

 import org.eclipse.ui.navigator.INavigatorContentService;

 /**
  * Caches instances of {@link INavigatorContentService} to facilitate the
  * handling of drop operations in other viewers.
  *
  * @since 3.2
  *
  */
 public class NavigatorContentServiceTransfer {
     
     private static final NavigatorContentServiceTransfer instance = new NavigatorContentServiceTransfer();
     
     /**
      *
      * @return The singleton instance of the transfer service.
      */
     public static NavigatorContentServiceTransfer getInstance() {
         return instance;
     }

     private final Set registeredContentServices = new HashSet ();
     
     /**
      *
      * @param aContentService The Content Service to register.
      */
     public synchronized void registerContentService(INavigatorContentService aContentService) {
         if(findService(aContentService.getViewerId()) == null) {
             registeredContentServices.add(new WeakReference (aContentService));
         }
     }
     
     /**
      *
      * @param aContentService The Content Service to unregister.
      */
     public synchronized void unregisterContentService(INavigatorContentService aContentService) {
   
         for (Iterator iter = registeredContentServices.iterator(); iter.hasNext();) {
             WeakReference ref = (WeakReference ) iter.next();
             if(ref.get() == null) {
                 iter.remove();
             } else {
                 if(ref.get() == aContentService) {
                     iter.remove();
                     return;
                 }
             }
         }
     }
     
     /**
      *
      * @param aViewerId A viewer id that should have previously been registered with the service.
      * @return The registered content service for the given viewer id.
      */
     public synchronized INavigatorContentService findService(String aViewerId) {
         if(aViewerId == null || aViewerId.length() == 0) {
             return null;
         }
         INavigatorContentService contentService;
         for (Iterator iter = registeredContentServices.iterator(); iter.hasNext();) {
             WeakReference ref = (WeakReference ) iter.next();
             if(ref.get() == null) {
                 iter.remove();
             } else {
                 contentService = (INavigatorContentService)ref.get();
                 if(aViewerId.equals(contentService.getViewerId())) {
                     return contentService;
                 }
             }
         }
         return null;
     }
     

 }

